Modification of copper/iron selectivity in copper solvent extraction systems

ABSTRACT

A solvent extraction composition comprising one or more orthohydroxyarylaldoximes and/or one or more orthohydroxyarylketoximes, and one or more selectivity modifiers consisting of phosphinic and/or phosphonic acids, and salts and esters therefore and optionally one or more equilibrium modifiers is provided.

The present invention concerns a solvent extraction composition, asolvent extraction process and especially a process for the extractionof metals, particularly copper and iron, from aqueous solutions,especially solutions obtained by leaching ores.

It is known to extract metals, especially copper and to a much lesserdegree iron, from aqueous solutions containing the metals in the formof, for example, salts, by contacting the aqueous solution with asolution of a solvent extractant in a water immiscible organic solventand then separating the solvent phase loaded with the metals, i.e.containing at least a part of the metals in the form of a complex Themetals can then be recovered by stripping with a solution of lower pH(the electrolyte) followed for example, by electrowinning. Mostcommonly, the aqueous metal-containing solutions for extraction are theresult of the acid leaching of ores.

Solvent extractants which have found favour in recent years particularlyfor the recovery of copper from aqueous solutions include oximereagents, especially o-hydroxyarylaldoximes and o-hydroxyarylketoximes.The oxime reagents exhibit a high degree of selectivity of copper overiron which is commonly expressed as the transfer ratio. The transferratio is the ratio of the loaded organic copper concentration minus thestripped organic copper concentration divided by the loaded organic ironconcentration minus the stripped organic iron concentration. Although ahigh transfer ratio is usually desired, the presence of some iron in theelectroyte can also have benefits as described in for example US patentapplication 2005/0023151. In some cases iron is desired as a counter ionto maintain a certain EMF value in the electrolyte. The selectivity ofcopper over iron is a function of the metal extractant, the metal andacid concentrations in the leach solution and electrolyte, and theoperating conditions in the solvent extraction plant. In many instancesusing the present copper solvent extractants the selectivity of copperover iron is such that insufficient iron is transferred to theelectrolyte via the organic phase to maintain the concentration rangerequired. In such cases iron sulphate is added to the electrolyte toachieve the desired concentration.

Using the solvent extraction process it is common for other impuritiesto be transferred to the electrolyte by a physical means. Impuritiestransferred to the strip solution will eventually build up in thecircuit and have a negative impact on the electrowinning step. For thatreason, operations often bleed a portion of the electrolyte to controlthe build up of impurities. In those cases, the electrolyte must bereplaced with fresh water, acid, and iron (usually as ferrous sulphate).In some cases the amount of iron which must be added to make up for thatwhich is lost in the bleed can be excessive. The addition of iron cannegatively effect the economics of an operation. For these reasons itwould be highly desirable to have a solvent extractant formulation whichwould allow an operation to achieve a desired transfer ratio—withoutlosing the well know benefits of the hydroxyl oxime formulationscommonly used today.

Although there are many chelating reagents which have a higher affinityfor iron than the hydroxy oximes, It has surprisingly been found thatthe addition of small quantities of a select few iron chelating reagents(hereafter referred to as selectivity modifiers) to oxime reagents has aprofound effect on the copper over iron selectivity characteristics ofthe resulting extractant composition. This effect on the resultingcopper:iron transfer ration is significantly greater than the effect ofthe sum of the two products when used independently.

According to a first aspect of the present invention, there is provideda solvent extraction composition comprising one or moreorthohydroxyarylaldoximes and/or one or more orthohydroxyarylketoximes,one or more selectivity modifiers consisting of phosphinic and/orphosphonic acids, salts or esters therefore, and optionally one or moreequilibrium modifiers. The selectivity modifiers are preferably presentin a molar ratio of the o-hydoxy oxime:selectivity modifier from about0.001 to 0.05. The compositions preferably also comprise a waterimmiscible organic solvent.

Compositions according to the present invention may facilitate increasediron transfer in solvent extraction circuits. Higher iron transfer canbe translated into a decrease in the use of iron sulphate addition tothe electrolyte to maintain a target electrolyte iron concentration.Compositions according to the present invention may find particular usewith processes which require electrolyte iron concentrationssignificantly above the conventional range.

The orthohydroxyarylketoxime compounds employed in the present inventionare substantially water insoluble and preferably have the formula:

Formula (1)wherein

R¹ is an optionally substituted hydrocarbyl group

R² is an optionally substituted ortho-hydroxyaryl group,

and salts thereof.

The orthohydroxyarylaldoxime compounds employed in the present inventionare substantially water insoluble and preferably have the formula:

Formula (2)wherein

R³ is an optionally substituted ortho-hydroxyaryl group,

and salts thereof.

Whilst the invention is described herein with reference to compounds ofFormula (1) and (2), it is understood that it relates to said compoundin any possible tautomeric forms, and also the complexes formed betweenorthohydroxyarylaldoximes or orthohydroxyarylketoximes and metals,particularly copper.

Optionally substituted hydrocarbyl groups which may be represented by R¹preferably comprise optionally substituted alkyl and aryl groupsincluding combinations of these, such as optionally substituted aralkyland alkaryl groups.

Examples of optionally substituted alkyl groups which may be representedby R¹ include groups in which the alkyl moieties can contain from 1 to20, especially from 1 to 4, carbon atoms. A preferredorthohydroxyarylketoxime is one in which R¹ is alkyl, preferablycontaining up to 20, and especially up to 10, and more preferably up to3 saturated aliphatic carbon atoms, and most preferably R¹ is a methylgroup.

Examples of optionally substituted aryl groups which may be representedby R¹ include optionally substituted phenyl groups. When R¹ is an arylgroup, it is preferably an unsubstituted phenyl group.

The orthohydroxyarylaldoximes and orthohydroxyarylketoximes are oftenpresent in a total amount of up to 70% by weight of the composition,commonly no more than 60%, and usually no more than 50% w/w. Often, thetotal amount of orthohydroxyarylaldoxime and orthohydroxyarylketoxime inuse comprises at least 1% by weight, commonly at least 2.5% by weightand usually at least 5% by weight of composition, and preferablycomprises from 7.5 to 20%, such as about 10%, by weight of thecomposition.

The criteria for selectivity modifier selection is stringent as thechemistry used must have no detrimental effect on the copper solventextraction process. More specifically, the selectivity modifier must notinterfere with copper transfer; it must be selective over other metalslikely to be present in significant concentration in the leach solution;it must not have a detrimental affect on kinetic performance; it mustnot have a detrimental affect on stability of the extractant, and itmust not be detrimental to the physical performance of the organicphase. The selectivity modifiers employed in the present invention aresubstantially water insoluble phosphinic and phosphonic acids, or saltsor esters therefore. Preferred selectivety modifiers are selected fromthe group of phosphinic acids, or salts or esters thereof of the formulaR₄R₅P(O)OR₆ where R₄ is H, C1-C20 alkyl, aryl or arylalkyl group R₅ isH, C1-C20 alkyl, aryl or arylalkyl group, and R₆ is H, a metal cation orNR₇4 where R₇ is H, a C1-C20 alkyl, aryl or arylalkyl group, orphosphonic acids or salts or esters thereof of the formula R₈R₉OP(O)OR₁₀where R₈ is H, C1-C20 alkyl, aryl or arylalkyl group, R₉ is H, C1-C20alkyl, aryl or arylalkyl group, and R₁₀ is H, a metal cation, or NR₇4where R₇ is H, C1-C20 alkyl, aryl or arylalkyl group. Examples ofsuitable phosphinic acids include bis(2,4,4-trimethyl)phosphinic acidand bis(2-ethylhexyl)phosphinic acid or their salts. Examples ofsuitable phosphonic acids include bis(2-ethylhexyl)phosphonic acid andphenylphosphonic acid or their salts. Examples of suitable phosphonicacids esters include 2-ethylhexylphosphonic acid, mono-2-ethylhexylester. The selectivity modifier preferably is present in a molar ratioof the o-hydoxyoxime:selectivity modifier from about 0.001 to 0.05.

Equilibrium modifiers employed in the present invention aresubstantially water insoluble. Suitable equilibrium modifiers can bealkylphenols, alcohols, esters, ethers and polyethers, carbonates,ketones, nitrites, amides, carbamates, sulphoxides, and salts of aminesand quaternary ammonium compounds.

Organic solvents which may be present in the composition include anymobile organic solvent, or mixture of solvents, which is immiscible withwater and is inert under the extraction conditions to the othermaterials present. Preferably the organic solvent has a low aromatichydrocarbon content.

Preferred organic solvents are hydrocarbon solvents which includealiphatic, alicyclic and aromatic hydrocarbons and mixtures thereof aswell as chlorinated hydrocarbons such as trichloroethylene,perchloroethylene, trichloroethane and chloroform.

Highly preferred organic solvents having a low aromatics content includesolvents and solvent mixtures where the amount of aromatic hydrocarbonspresent in the organic solvent is less than 30%, usually around 23% orless, often less than 5%, and frequently less than 1%.

Examples of suitable hydrocarbon solvents include ESCAID 110, ESCAID115, ESCAID 120, ESCAID 200, and ESCAID 300 commercially available fromExxon (ESCAID is a trade mark), SHELLSOL D70 and D80 300 commerciallyavailable from Shell (SHELLSOL is a trade mark), and CONOCO 170commercially available from Conoco (CONOCO is a trade mark). Suitablesolvents are hydrocarbon solvents include high flash point solvents andsolvents with a high aromatic content such as SOLVESSO 150 commerciallyavailable from Exxon (SOLVESSO is a trade mark).

More preferred are solvents with a low aromatic content. Certainsuitable solvents with a low aromatic content, have aromatic contents of<1% w/w, for example, hydrocarbon solvents such as ESCAID 110commercially available from Exxon (ESCAID is a trade mark), and ORFOM SX10 and ORFOM SX11 commercially available from Phillips Petroleum (ORFOMis a trade mark). Especially preferred, however on grounds of lowtoxicity and wide availability, are hydrocarbon solvents of relativelylow aromatic content such as kerosene, for example ESCAID 100 which is apetroleum distillate with a total aromatic content of 23% commerciallyavailable from Exxon (ESCAID is a trade mark), or ORFOM SX7,commercially available from Phillips Petroleum (ORFOM is a trade mark).

In many embodiments, the composition comprises at least 30%, often atleast 45% by weight, preferably from 50 to 95% w/w of water-immisciblehydrocarbon solvent. Advantageously, it may be preferred to make andsupply the composition in the form of a concentrate. The concentrate maythen be diluted by the addition of organic solvents as described hereinabove to produce compositions in the ranges as described herein above.Where the concentrate contains a solvent, it is preferred that the samesolvent is used to dilute the concentrate to the “in use” concentrationrange. In many embodiments, the concentrate composition comprises up to30%, often up to 20% by weight, preferably up to 10% w/w ofwater-immiscible hydrocarbon solvent. Often the concentrate compositioncomprises greater than 5% w/w of water-immiscible hydrocarbon solvent.In certain high strength concentrates it may be necessary to employ ahigher than normal aromatic hydrocarbon content. In such cases where ahigh aromatic hydrocarbon containing solvent is used in the concentrate,solvent of very low aromatic hydrocarbon content may be used to dilutethe concentrate to the “in use” concentration range.

Examples of suitable solvent extraction compositions are those whichcomprise one of the following:

1) Blends of 5-(C₈ to C₁₄ alkyl)-2-hydroxybenzaldoxime and 5-(C₈ to C₁₄alkyl)-2-hydroxyacetophenone oxime in a weight ratio of from about 90:10to about 50:50 aldoxime to ketoxime, and/or optionally one or moremodifiers selected from 2,2,4-trimethyl-1,3-pentanediolmono-isobutyrate, 2,2,4-trimethyl-1,3-pentanediol mono-benzoate,2,2,4-trimethyl-1,3-pentanediol di-isobutyrate,2,2,4-trimethyl-1,3-pentanediol di-benzoate, butyl adipate, pentyladipate, hexyl adipate, isobutyl heptyl ketone, nonanone, diundecylketone, 5,8-diethyldodecane-6,7-dione, tridecanol, tetraethyleglycoldi-2-ethylhexanoate, and nonyl phenol, and a selectivity modifierselected from bis(2,4,4-trimethylpently)phosphinic acid or2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester, present as a molarratio of the o-hydoxyoxime:selectivity modifier from about 0.001 to0.05.

2) Blends of 5-(C₈ to C₁₄ alkyl)-2-hydroxybenzaldoxime or 5-(C₈ to C₁₄alkyl)-2-hydroxyacetophenone oxime, optionally one or more modifiersselected from 2,2,4-trimethyl-1,3-pentanediol mono-isobutyrate,2,2,4-trimethyl-1,3-pentanediol mono-benzoate,2,2,4-trimethyl-1,3-pentanediol di-isobutyrate,2,2,4-trimethyl-1,3-pentanediol di-benzoate, butyl adipate, pentyladipate, hexyl adipate, isobutyl heptyl ketone, nonanone, diundecylketone, 5,8-diethyldodecane-6,7-dione, tridecanol, and nonyl phenol, anda selectivity modifier selected frombis(2,4,4-trimethylpently)phosphinic acid or 2-ethylhexylphosphonicacid, mono-2-ethylhexyl ester, present as a molar ratio of theo-hydoxyoxime:selectivity modifier from about 0.001 to 0.05.

According to a second aspect of the present invention, there is provideda process for the extraction of a metal from solution in which an acidicsolution containing a dissolved metal is contacted with a solventextraction composition, whereby at least a fraction of the metal isextracted into the organic solution, characterised in that the solventextraction composition comprises a water immiscible organic solvent, oneor more orthohydroxyarylaldoximes and one or moreorthohydroxyarylketoximes, and a selectivity modifier present in a molarratio of the o-hydoxyoxime from about 0.001 to 0.05.

Metals that may be extracted in the process according to the secondaspect of the present invention include copper, iron, cobalt, nickel,manganese and zinc, most preferably copper.

The orthohydroxyarylaldoximes, orthohydroxyarylketoximes, theequilibrium modifiers, the selectivity modifiers and the waterimmiscible organic solvent are as herein described above.

The aqueous acidic solution from which metals are extracted by theprocess of the second aspect of the present invention often has a pH inthe range of from −1 to 7, preferably from 0 to 5, and most preferablyfrom 0.25 to 3.5. The solution can be derived from the leaching of oresor may be obtained from other sources, for example metal containingwaste streams

The concentration of metal, particularly copper, in the aqueous acidicsolution will vary widely depending for example on the source of thesolution. Where the solution is derived from the leaching of ores, themetal concentration is often up to 75 g/l and most often from 1 to 40g/l.

The process of the second aspect of the present invention can be carriedout by contacting the solvent extractant composition with the aqueousacidic solution. Ambient or elevated temperatures, such as up to 75° C.can be employed if desired. Often a temperature in the range of from 5to 60° C., and preferably from 15 to 40° C., is employed. The aqueoussolution and the solvent extractant are usually agitated together tomaximise the interfacial areas between the two solutions. The volumeratio of solvent extractant to aqueous solution are commonly in therange of from 20:1 to 1:20, and preferably in the range of from 5:1 to1:5. In many embodiments, to reduce plant size and to maximise the useof solvent extractant, organic to aqueous volume ratios close to 1:1 aremaintained by recycle of one of the streams.

After contact with the aqueous acidic solution, the metal can berecovered from the solvent extractant by contact with an aqueous acidicstrip solution.

The aqueous strip solution employed in the process according to thesecond aspect of the present invention is usually acidic, commonlyhaving a pH of 2 or less, and preferably a pH of 1 or less, for example,a pH in the range of from −1 to 0.5. The strip solution commonlycomprises a mineral acid, particularly sulphuric acid, nitric acid orhydrochloric acid. In many embodiments, acid concentrations,particularly for sulphuric acid, in the range of from 130 to 200 g/l andpreferably from 150 to 180 g/l are employed. When the extracted metal iscopper, preferred strip solutions comprise stripped or spent electrolytefrom a copper electro-winning cell, typically comprising up to 80 g/lcopper, often greater than 20 g/l copper and preferably from 30 to 70g/l copper, and up to 220 g/l sulphuric acid, often greater than 120 g/lsulphuric acid, and preferably from 150 to 180 g/l sulphuric acid.

The volume ratio of organic solution to aqueous strip solution in theprocess of the second aspect of the present invention is commonlyselected to be such so as to achieve transfer, per liter of stripsolution, of up to 50 g/l of metal, especially copper into the stripsolution from the organic solution. In many industrial copperelectrowinning processes transfer is often from 10 g/l to 35 g/l, andpreferably from 15 to 20 g/l of copper per liter of strip solution istransferred from the organic solution. Volume ratios of organic solutionto aqueous solution of from 1:2 to 15:1 and preferably from 1:1 to 10:1,especially less than 6:1 are commonly employed.

Both the separation and stripping process can be carried out by aconventional batch extraction technique or column contactors or by acontinuous mixer settler technique. The latter technique is generallypreferred as it recycles the stripped organic phase in a continuousmanner, thus allowing the one volume of organic reagent to be repeatedlyused for metal recovery.

A preferred embodiment of the second aspect of the present inventioncomprises a process for the extraction of a metal from aqueous acidicsolution in which:

in step 1, the solvent extraction composition comprising a waterimmiscible organic solvent, one or more orthohydroxyarylaldoximes and/orone or more orthohydroxyarylketoximes, and one or more equilibriummodifiers and a selectivity modifier is first contacted with the aqueousacidic solution containing metal,

in step 2, separating the solvent extraction composition containingmetal-solvent extractant complex from the aqueous acidic solution;

in step 3, contacting the solvent extraction composition containingmetal-solvent extractant complex with an aqueous acidic strip solutionto effect the stripping of the metal from the water immiscible phase;

in step 4, separating the metal-depleted solvent extraction compositionfrom the loaded aqueous strip solution.

The invention is further illustrated, but not limited, by the followingexamples.

EXAMPLES Example 1

Extractant compositions were prepared as described in the followingtable. 150 ml of each of the extractant compositions was then stirredwith 150 ml of an aqueous “extraction” solution containing 1.8 g/l Cu,1.0 g/l Fe (of which 0.042 g/l was Fe(III)) & pH 2.1. The aqueous andorganic were stirred for 3 min to simulate extraction. After 3 min theextractant compositions were separated, and the organic was sampled. Themetal loaded extractant was then mixed with 30 ml of an aqueous “strip”solution containing 35.3 g/l Cu and 179 g/l of sulphuric acid for 3minutes. After separation the extractant compositions were sampled. Thesamples of the organic phase were then analysed for copper and ironcontent. The table below shows the results for each extractantcomposition in terms of Transfer ratio.

Org. Org. Cu/Fe Cu Fe % Cu Transfer Extractant Composition Cycle (g/l)(g/l) Strip Ratio Cu/Fe A 0.179 M 2-hydroxy-5- Load 4.77 0.00063 55.144696 nonylsalicylaldoxime + Strip 2.14 0.00007 0.1 M2,2,4-trimethyl-1,3- pentanediol di-isobutyrate In kerosene B 0.00179 MBis(2,4,4- Load 0.001 0.0051 0.00 0 trimethyl)phosphinic acid Strip0.001 0.00116 In kerosene C 0.179 M 2-hydroxy-5- Load 4.71 0.069 55.84132 nonylsalicylaldoxime + Strip 2.08 0.049 0.1 M 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate + 0.00179 M Bis(2,4,4- trimethyl)phosphinicacid In kerosene D 0.179 M 2-hydroxy-5- Load 4.28 0.0014 46.96 2051nonylacetophenone oxime Strip 2.27 0.00042 In kerosene E 0.179 M2-hydroxy-5- Load 3.82 0.0628 66.23 173 nonylacetophenone oxime + Strip1.29 0.0482 0.00179 M Bis(2,4,4- trimethyl)phosphinic acid In kerosene

As shown neither the modified aldoxime (A), nor the ketoxime (D) wascapable of transferring significant amounts of iron in the presence ofcopper. The phosphinic acid (B) transferred some iron without copper,however the blend of oxime with phosphinic acid (Examples C and E)transferred significantly more iron than would be expected relative tothe individual components. Transfer ratios dropped from over 2000:1 toless than 200:1 without impacting copper transfer.

The increased iron transfer and corresponding lower Cu:Fe transfer ratiowas achieved without impact to the stability of the oxime, or othernegative physical or metallurgical effects.

Example 2

Extractant compositions were prepared by mixing aliquots of2-hydroxy-5-nonylsalicylaldoxime (an aldoxime) &2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (a modifier) with varyingmasses of Tributyl Phosphite (TBP). In each case 11.76 g (0.179M) ofaldoxime, 7.23 g (0.1M) of modifier and 0 g (Blank); 0.118 g (0.00179M)& 1.18 g (0.0179M) of TBP (95% purity) was made up to 0.25 liter withOrfom SX7 (a diluent).

200 ml of the extractant composition was then stirred with 200 ml of anaqueous “extraction” solution containing 3.5 g/l Cu, 3.8 g/l Fe (ofwhich 1.0 g/l was Fe(III)) & pH 2.1 for 30 min to simulate extraction.After 30 min the extractant composition was separated from the aqueousand sampled. The extractant formulation was then stirred for a further30 minutes with 40 ml of an aqueous “strip” solution containing 35.3 g/lCu and 179 g/l of sulphuric acid. After separation the extractantcomposition was sampled. The samples of the organic phase were thenanalysed for copper and iron content. The table below shows the resultsfor 100:1 and 10:1 molar ratios of aldoxime to potential selectivitymodifier.

Org. Cu Org. Fe Transfer Cycle (g/l) (g/l) Ratio 0.179 M 2-hydroxy-5-Load 5.22 0.0022 1275 nonylsalicylaldoxime + Strip 2.44 0.00002 0.1 M2,2,4-trimethyl-1,3- pentanediol di-isobutyrate (BLANK) +BLANK + 0.0179M TBP Load 4.99 0.0029 961 Strip 2.55 0.00036 +BLANK + 0.00179 M TBPLoad 5.31 0.00153 1986 Strip 2.51 0.00012

As shown TBP is surprisingly not suitable as a selectivity modifier anddid not enhance iron transfer relative to the ‘BLANK’ extractantcomposition.

Example 3

Extractant compositions were prepared by mixing aliquots of2-hydroxy-5-nonylsalicylaldoxime (an aldoxime) &2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (a modifier) with varyingmasses of Di(2-ethylhexyl) phosphoric acid (DEHPA). In each case 11.76 g(0.179M) of aldoxime, 7.23 g (0.1M) of modifier and 0 g (Blank); 0.149 g(0.00179M) & 1.49 g (0.0179M) of DEHPA (97% purity) was made up to 0.25liter with Orfom SX7 (a diluent).

200 ml of the extractant composition was then stirred with 200 ml of anaqueous “extraction” solution containing 3.5 g/l Cu, 3.8 g/l Fe (ofwhich 1.0 g/l was Fe(III)) & pH 2.1 for 30 min to simulate extraction.After 30 min the extractant composition was separated and sampled. Theextractant composition was then stirred for a further 30 minutes with 40ml of an aqueous “strip” solution containing 35.3 g/l Cu and 179 g/l ofsulphuric acid. After separation the extractant composition was sampled.The samples of the organic phase were then analysed for copper and ironcontent. The table below shows the results for 100:1 and 10:1 molarratios of aldoxime to potential selectivity modifier.

Cycle Org. Cu Org. Fe Transfer 3 (g/l) (g/l) Ratio 0.179 M 2-hydroxy-5-Load 5.22 0.0022 1275 nonylsalicylaldoxime + Strip 2.44 0.00002 0.1 M2,2,4-trimethyl- 1,3-pentanediol di- isobutyrate (BLANK) +BLANK + 0.0179M Load 4.42 0.549 14 DEHPA Strip 2.1 0.386 +BLANK + 0.00179 M Load 5.220.075 151 DEHPA Strip 2.8 0.059

Although the addition of DEHPA succeeded in reducing the Cu:Fe transferratio, the amount of iron remaining in the organic phase following thestrip cycle was greater than 70%. On repetition of the experiment it wasdetermined DEHPA loads readily but does not strip easily—using standardstrength electrolyte. DEHPA is therefore effectively poisoned by ironand therefore unsuitable as a selectivity modifier.

Example 4

Extractant compositions were prepared by mixing aliquots of2-hydroxy-5-nonylsalicylaldoxime (an aldoxime) &2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (a modifier) with varyingmasses of Acorga SBX-50. SBX-50 is a mixture of which is a mixture ofisooctadecyl-phosphoric and di-isooctadecyl-phosphoric acids. In eachcase 11.76 g (0.179M) of aldoxime, 7.23 g (0.1M) of modifier and 0 g(Blank); 0.199 g (0.00179M) & 1.99 g (0.0179M) of SBX-50 (90% purity)was made up to 0.25 liter with Orfom SX7 (a diluent). 200 ml of theextractant composition was then stirred with 200 ml of an aqueous“extraction” solution containing 3.5 g/l Cu, 3.8 g/l Fe (of which 1.0g/l was Fe(III)) & pH 2.1 for 30 min to simulate extraction. After 30min the extractant composition was separated and sampled. The extractantcomposition was then stirred for a further 30 minutes with 40 ml of anaqueous “strip” solution containing 35.3 g/l Cu and 179 g/l of sulphuricacid. After separation the extractant composition was sampled. Thesamples of the organic phase were then analysed for copper and ironcontent. The table below shows the results for 100:1 and 10:1 molarratios of aldoxime to potential selectivity modifier.

Org. Cu Org. Fe Transfer Cycle (g/l) (g/l) Ratio 0.179 M 2-hydroxy-5-Load 5.22 0.0022 1275 nonylsalicylaldoxime + Strip 2.44 0.00002 0.1 M2,2,4-trimethyl-1,3- pentanediol di-isobutyrate (BLANK) +BLANK + 0.0179M Load 4.9 0.607 39 SBX-50 Strip 2.18 0.538 +BLANK + 0.00179 M Load 5.210.076 130 SBX-50 Strip 2.47 0.0549

Again the example shows that the extractant formulations containingSBX-50 are poisoned by iron. The iron loads readily but does not stripeasily. SBX-50 is therefore unsuitable as a selectivity modifier.

Example 5

Extractant compositions were prepared by mixing aliquots of2-hydroxy-5-nonylsalicylaldoxime (an aldoxime) &2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (a modifier) with varyingmasses of tris (2-ethylhexyl)amine (TEHA). In each case 11.76 g (0.179M)of aldoxime, 7.23 g (0.1M) of modifier and 0 g (Blank); 0.16 g(0.00179M) of TEHA was made up to 0.25 liter with Orfom SX7 (a diluent).

200 ml of the extractant composition was then stirred with 200 ml of anaqueous “extraction” solution containing 3.5 g/l Cu, 3.8 g/l Fe (ofwhich 1.0 g/l was Fe(III)) & pH 2.1 for 30 min to simulate extraction.After 30 min the extractant composition was separated and sampled. Theextractant composition was then stirred for a further 30 minutes with 40ml of an aqueous “strip” solution containing 35.3 g/l Cu and 179 g/l ofsulphuric acid. After separation the extractant composition was sampled.The samples of the organic phase were then analysed for copper and ironcontent. The table below shows the results for 100:1 and 10:1 molarratios of aldoxime to potential selectivity modifier.

Org. Cu Org. Fe Transfer Cycle 3 (g/l) (g/l) Ratio Blank Load 5.220.0022 1275 +0.00179 M Load 5.12 0.00254 1073 TEHA Strip 2.48 0.00008

As shown TEHA (a known iron extractant) does not complex iron readilyunder the test conditions and is therefore unsuitable as a selectivitymodifier.

Example 6

Extractant compositions were prepared by mixing aliquots of2-hydroxy-5-nonylsalicylaldoxime (an aldoxime) &2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (a modifier) with varyingmasses of dinonylnaphthalene sulfonic acid (DNNSA)—a known irontransferring agent. In each case 11.76 g (0.179M) of aldoxime, 7.23 g(0.1M) of modifier and 0 g (Blank) & 0.16 g (0.00179M) of DNNSA was madeup to 0.25 liter with Orfom SX7 (a diluent).

Accelerated degradation tests were carried out on the extractantcompositions. 250 ml of each extractant composition was mixed with anaqueous solution containing 30.0 g/l of copper and 179 g/l of sulphuricacid for 284 hours at 60° C. samples were taken periodically and therate constants calculated.

K = (hr-1) 0.179 M 2-hydroxy-5-nonylsalicylaldoxime + 0.000651 0.1 M2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (BLANK) +BLANK + 0.00179M DNNSA 0.012352

Although DNNSA is known to extract iron under the test conditions—informulation with an oxime extractant it is not suitable as a“selectivity modifier”. The example demonstrates that the degradationrate of the extractant formulation containing DNNSA was several order ofmagnituted greater than the Blank. DNNSA would therefore be unsuitableas a selectivity modifier.

Example 7

Extractant compositions were prepared by mixing aliquots of2-hydroxy-5-nonylsalicylaldoxime (an aldoxime) &2,2,4-trimethyl-1,3-pentanediol di-isobutyrate (an equilibrium modifier)with varying masses of phosphinic and phosphonic selectivity modifiers.In each case 47.1 g of aldoxime, 28.64 g of modifier and 0.00179M ofeach potential selectivity modifier was made up to 1.0 liter with OrfomSX7 (a diluent).

100 ml of the extractant composition was then stirred with 300 ml of anaqueous “extraction” solution containing 1.43 g/l Cu, 7.91 g/l Fe & pH2.0 for 30 min to simulate extraction. After 30 min the extractantcomposition was separated and sampled. The extractant composition wasthen stirred for a further 30 minutes with 20 ml of an aqueous “strip”solution containing 35.6 g/l Cu, 3.1 g/l Fe and 179 g/l of sulphuricacid. After separation the extractant composition was sampled. Thesamples of the organic phase were then analysed for copper and ironcontent. The table below shows the results for a 100:1 molar ratio ofaldoxime to selectivity modifier.

Org. Org. Cu Fe Transfer Cycle (g/l) (g/l) Ratio Aldoxime + Load 5.190.0034 726 EquilibriumModifier Strip 3.23 0.0007 +Aldoxime + EquilibriumLoad 5.04 0.096 43 Modifier + Bis(2,4,4- Strip 3.18 0.053trimethyl)phosphinic acid, Aldoxime + Equilibrium Load 5.04 0.093 53Modifier + Strip 3.18 0.058 2-ethylhexylphosphonic acid,mono-2-ethylhexyl ester,

The example demonstrates that both Bis(2,4,4-trimethyl)phosphinic acidand 2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester would besuitable selectivity modifiers.

Example 8

High Ratio of 2-Hydroxy-5-Nonylsalicylaldoxime to Selectivity Modifier

Extractant compositions A, B & C were prepared as described in thefollowing table. 50 ml of each of the extractant compositions wasstirred with 150 ml of an aqueous “extraction” solution containing 5.0g/l Cu, 0.2 g/l Fe (III)), pH 1.74 for 3 min to simulate extraction.After extraction the extractant compositions were separated, and thenmixed for a further 3 minutes with 25 ml of an aqueous “strip” solutioncontaining 32.5 g/l Cu and 176 g/l of sulfuric acid. After separationthe aqueous phase was discarded and the extraction and strip proceduresrepeated a further two times. The ratio of extractant composition toaqueous “extraction” solution was 1:2 for the second and third contacts.The ratio of extractant composition to “strip” solution was 2:1 for thesecond and third contacts. After the third cycle samples of the organicand aqueous phases were taken and copper and iron concentration in eachmeasured. The table below shows the results after the third cycle.

Crg. Org. Cu Cu/Fe Cu/Fe Cu Cu Fe Strip Rejection Transfer TransferExtractant Composition Cycle (g/l) (g/l) (%) Ratio Ratio (g/l) A 0.365 M2-hydroxy-5-nonylsalicylaldoxime + Load 7.72 0.00029 26621 17040 4.30.268 M 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate Strip 3.460.00004 55.2 B 0.365 M 2-hydroxy-5-nonylsalicylaldoxime + Load 8.150.00074 57.1 11014 6940 4.7 0.268 M 2,2,4-trimethyl-1,3-pentanedioldi-isobutyrate + Strip 3.5 0.00007 0.000073 MBis(2,4,4-trimethylpentyl)phosphinic acid C 0.365 M2-hydroxy-5-nonylsalicylaldoxime + Load 8.78 0.00106 56.2 8283 5135 4.90.268 M 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate + Strip 3.850.0001 0.000073 M 2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester

Formulation composition A contained no selectivity modifier and underthe test conditions a Cu/Fe transfer ratio of 17040 was obtained.Formulation composition B included the addition of the selectivitymodifier bis(2,4,4-trimethylpentyl)phosphinic acid to achieve a molarratio of a ratio of 2-hydroxy-5-nonylsalicylaldoxime tobis(2,4,4-trimethylpentyl)phosphinic acid of 5000:1. Under the same testconditions as for A, the Cu/Fe Transfer Ratio of B decreased to 6940from 17040.

Formulation composition C included the addition of2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester to achieve a molarratio of 2-hydroxy-5-nonylsalicylaldoxime to 2-ethylhexylphosphonicacid, mono-2-ethylhexyl ester of 5000:1. Under the test conditions asfor A, the Cu/Fe transfer ratio of C decreased from to 5135 from 17040.

Example 9

High Ratio of2-Hydroxy-5-Nonylsalicylaldoxime+2-Hydroxy-5-Nonylacetophenone Oxime toSelectivity Modifier.

Extractant compositions A, B & C were prepared as described in thefollowing table. 50 ml of each of the extractant compositions wasstirred with 150 ml of an aqueous “extraction” solution containing 7.0g/l Cu, 0.2 g/l Fe (III)), pH 1.74 for 3 min to simulate extraction.After extraction the extractant compositions were separated, and thenmixed for a further 3 minutes with 25 ml of an aqueous “strip” solutioncontaining 32.5 g/l Cu and 176 g/l of sulfuric acid. After separationthe aqueous phase was discarded and the extraction and strip proceduresrepeated a further two times. The ratio of extractant composition toaqueous “extraction” solution was 1:2 for the second and third contacts.The ratio of extractant composition to “strip” solution was 2:1 for thesecond and third contacts. After the third cycle samples of the organicand aqueous phases were taken and copper and iron concentration in eachmeasured. The table below shows the results after the third cycle.

Crg. Org. Cu Cu/Fe Cu/Fe Cu Cu Fe Strip Rejection Transfer TransferExtractant Composition Cycle (g/l) (g/l) (%) Ratio Ratio (g/l) A 0.18 M2-hydroxy-5-nonylsalicylaldoxime + Load 8.85 0.00053 55.6 16698 223644.9 0.17 M 2-hydroxy-5-nonylacetophenone oxime Strip 3.93 0.00031 B 0.18M 2-hydroxy-5-nonylsalicylaldoxime + Load 8.92 0.0039 56.6 2287 1573 5.10.17 M 2-hydroxy-5-nonylacetophenone oxime + Strip 3.87 0.00069 0.00035M Bis(2,4,4-trimethylpentyl) phosphinic acid C 0.18 M2-hydroxy-5-nonylsalicylaldoxime + Load 8.87 0.0044 57.3 2016 1261 5.10.17 M 2-hydroxy-5-nonylacetophenone oxime + Strip 3.79 0.00037 0.00035M 2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester

Formulation composition A contained no selectivity modifier and underthe test conditions a Cu/Fe transfer ratio of 22364 was obtained.Formulation composition B included the addition of the selectivitymodifier bis(2,4,4-trimethylpentyl)phosphinic acid to achieve a molarratio of a ratio of2-hydroxy-5-nonylsalicylaldoxime/2-hydroxy-5-nonylacetophenone oxime tobis(2,4,4-trimethylpentyl)phosphinic acid of 1000:1. Under the same testconditions as for A, the Cu/Fe Transfer Ratio of B decreased to 1573from 22364.

Formulation composition C included the addition of2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester to achieve a molarratio of 2-hydroxy-5-nonylsalicylaldoxime/2-hydroxy-5-nonylacetophenoneoxime to 2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester of 1000:1.Under the test conditions as for A, the Cu/Fe transfer ratio of Cdecreased to 1261 from 22364.

Example 10

10 Low Ratio of 2-Hydroxy-5-Nonylsalicylaldoxime to Selectivity Modifier

Extractant compositions D, E, F, G & H were prepared as described in thefollowing table. 50 ml of each of the extractant compositions wasstirred with 150 ml of an aqueous “extraction” solution containing 4.6g/l Cu, 0.8 g/l Fe (III)), pH 2.0 for 3 min to simulate extraction.After extraction the extractant compositions were separated, and thenmixed for a further 3 minutes with 25 ml of an aqueous “strip” solutioncontaining 35.0 g/l Cu and 181 g/l of sulfuric acid. After separationthe aqueous phase was discarded and the extraction and strip proceduresrepeated a further two times. The ratio of extractant composition toaqueous “extraction” solution was 1:2 for the second and third contacts.The ratio of extractant composition to “strip” solution was 2:1 for thesecond and third contacts. After the third cycle samples of the organicand aqueous phases were taken and copper and iron concentration in eachmeasured. The table below shows the results after the third cycle.

Crg. Org. Cu Cu/Fe Cu/Fe Cu Cu Fe Strip Rejection Transfer TransferExtractant Composition Cycle (g/l) (g/l) (%) Ratio Ratio (g/l) D 0.456 M2-hydroxy-5-nonylsalicylaldoxime + Load 11.05 0.0005 59.4 22100 164006.6 0.334 M 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate Strip 4.490.0001 E 0.456 M 2-hydroxy-5-nonylsalicylaldoxime + Load 7.9 0.71 74.711 32 5.9 0.334 M 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate + Strip2 0.52 0.228 M Bis(2,4,4-trimethylpentyl)phosphinic acid F 0.456 M2-hydroxy-5-nonylsalicylaldoxime + Load 9.3 0.37 64.7 25 34 6.0 0.334 M2,2,4-trimethyl-1,3-pentanediol di-isobutyrate + Strip 3.28 0.19 0.091 MBis(2,4,4-trimethylpentyl) phosphinic acid G 0.456 M2-hydroxy-5-nonylsalicylaldoxime + Load 8.3 2.85 71.1 3 19 5.9 0.334 M2,2,4-trimethyl-1,3-pentanediol di-isobutyrate + Strip 2.4 2.54 0.228 M2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester H 0.456 M2-hydroxy-5-nonylsalicylaldoxime + Load 9.88 1.37 63.7 7 20 6.3 0.334 M2,2,4-trimethyl-1,3-pentanediol di-isobutyrate + Strip 3.59 1.05 0.091 M2-ethylhexylphosphonic acid, mono-2-ethylhexyl ester

Formulation composition D contained no selectivity modifier and underthe test conditions a Cu/Fe transfer ratio of 16400 was obtained.Formulation E included the addition of the selectivity modifierbis(2,4,4-trimethylpentyl)phosphinic acid to achieve a molar ratio of2-hydroxy-5-nonylsalicylaldoxime to bis(2,4,4-trimethylpentyl)phosphinicacid of 2:1. Under the same test conditions as for D, the Cu/Fe TransferRatio of E decreased to 32 from 16400.

Formulation F included the addition of the selectivity modifierbis(2,4,4-trimethylpentyl)phosphinic acid to achieve a molar ratio of2-hydroxy-5-nonylsalicylaldoxime to bis(2,4,4-trimethylpentyl)phosphinicacid of 5:1. Under the same test conditions as for D, the Cu/Fe TransferRatio of F decreased to 34 from 16400.

Formulation G included the addition of the selectivity modifier2-ethylhexylphosphonic acid, mono 2-ethylhexyl ester to achieve a molarratio of 2-hydroxy-5-nonylsalicylaldoxime to 2-ethylhexylphosphonicacid, mono 2-ethylhexyl ester of 2:1. Under the same test conditions asfor D, the Cu/Fe Transfer Ratio of G decreased to 19 from 16400.

Formulation H included the addition of the selectivity modifier2-ethylhexylphosphonic acid, mono 2-ethylhexyl ester to achieve a molarratio of 2-hydroxy-5-nonylsalicylaldoxime to 2-ethylhexylphosphonicacid, mono 2-ethylhexyl ester of 5:1. Under the same test conditions asfor D, the Cu/Fe Transfer Ratio of H decreased to 20 from 16400.

1. A solvent extraction composition comprising: having a copper:irontransfer ratio between 34 and 1700 a) one or moreorthohydroxyarylaldoximes and/or one or more orthohydroxyarylketoximes;b) one or more selectivity modifiers chosen from one or more phosphinicacid and/or phosphonic acid, and salts and esters thereof; c) one ormore equilibrium modifiers selected from alkylphenols, alcohols, esters,ethers and polyethers, carbonates, ketones, nitriles, amides,carbamates, sulphoxides, and salts of amines and quaternary ammoniumcompounds; and d) a water immiscible organic solvent, wherein theselectivity modifier is present in a molar ratio of the o-hydroxyoximefrom 0.001 to 0.05.
 2. A solvent extraction composition according toclaim 1, wherein the phosphinic acid, or salts or esters thereof, ischosen from a compound according to formula R₄R₅P(O)OR₆ where each of R₄and R₅ is independently chosen from H, C₁-C₂₀ alkyl, aryl or arylalkylgroup, and R₆ is chosen from H, a metal cation or N(R₇)₄ where R₇ ischosen from H, C₁-C₂₀ alkyl, aryl or arylalkyl group, and wherein thephosphonic acid, or salts or esters thereof, is chosen from a compoundaccording to formula R₈R₉OP(O)OR₁₀ where each of R₈ and R₉ is chosenfrom H, C₁-C₂₀ alkyl, aryl or arylalkyl group, and R₁₀ is H, a metalcation, or N(R₇)₄ where R₇ is H, C₁-C₂₀ alkyl, aryl or arylalkyl group.3. A solvent extraction composition according to claim 1, wherein theselectivity modifier is chosen from bis(2,4,4-trimethylpentyl)phosphinicacid, bis(2-ethylhexyl)phosphinic acid, bis(2-ethylhexyl)phosphonicacid, phenylphosphonic acid or their salts and 2-ethylhexylphosphonicacid, mono-2-ethylhexyl ester.
 4. A solvent extraction compositionaccording to claim 3 wherein the selectivity modifier isbis(2,4,4-trimethylpentyl)phosphinic acid or 2-ethylhexylphosphonicacid, mono-2-ethylhexyl ester.
 5. A solvent extraction compositionaccording to claim 1, wherein the selectivity modifier is present in amolar ratio of the o-hydroxyoxime from about 0.001 to 0.01.
 6. A solventextraction composition according to claim 1, wherein theorthohydroxyarylketoxime is a 5-(C₈-C₁₄ alkyl)-2-hydroxyacetophenoneoxime, and the orthohydroxyarylaldoxime is a 5-(C₈-C₁₄alkyl)-2-hydroxybenzaldoxime.
 7. A solvent extraction compositionaccording to claim 1, wherein said one or more equilibrium modifiers ischosen from: 2,2,4-trimethyl-1,3-pentanediol mono-isobutyrate;2,2,4-trimethyl-1,3-pentanediol mono-benzoate;2,2,4-trimethyl-1,3-pentanediol di-isobutyrate;2,2,4-trimethyl-1,3-pentanediol di-benzoate; di-butyl adipate; di-pentyladipate; di-hexyl adipate; isobutyl heptyl ketone; nonanone;2,6,8-trimethyl-4-nonanone; diundecyl ketone;5,8-diethyldodecane-6,7-dione; tridecanol; tetraethyleneglycoldi-2-ethylhexanoate and nonyl phenol.
 8. A solvent extractioncomposition according to claim 7, wherein the orthohydroxyarylketoximeis 2-hydroxy-5-nonylacetophenone oxime, and the orthohydroxyarylaldoximeis 2-hydroxy-5-nonylsalicylaldoxime and equilibrium modifier is2,2,4-trimethyl-1,3-pentanediol di-isobutyrate.
 9. A solvent extractioncomposition according to claim 1, wherein the ratio oforthohydroxyarylaldoximes and/or one or more orthohydroxyarylketoximesto equilibrium modifier is from 5000:1 to about 2:1.